240 MANUAL OF VEGETABLE-GARDEN INSECTS 



burrow downward throiiii:li tlie center to the tuber. On reach- 

 ing the potato, its burrow becomes somewhat larger and winds 

 aimlessly through the flesh. The full-growm larva is about 

 yV inch in length, the body is white and the head yellowish 

 or brownish. The grubs become mature in two to three weeks. 

 The tissue surrounding the burrow becomes discolored and decay 

 sets in, giving the tuber a peculiar odor. When mature the 

 grub eats out an oval cavity and after resting a day or two 

 transforms into a white pupa about ^ to ^ inch in length. The 

 pupal period occupies five to eight days, and after waiting 

 two or three days to harden, the beetle eats its way oiit of the 

 pupal cell. The beetles may then either leave the potato or 

 may deposit eggs for another brood in the same tuber. Several 

 hundred lar\^ie may occupy the same potato and breeding may 

 continue until all food material has been destroyed. Gen- 

 eration after generation follow each other as long as food is 

 available, but the beetles are able to exist for a long period 

 without eating and resume reproductive activity w^hen food is 

 again available. The life cycle is completed, under favorable 

 conditions, in about a month. The beetles are rather general 

 feeders and are often found feeding on species of wild morning- 

 glory and it is believed they can breed in these plants. 



The sw^eet potato w^eevil is a most destructive pest and has 

 caused the abandonment of the growing of sweet potatoes in 

 many localities. It is especially injurious to the potatoes in 

 storage pits, where breeding may continue until the tubers are 

 entirely consumed. 



Control. 



Under conditions obtaining in the southern states, the in- 

 juries inflicted by this weevil may be prevented in large measure 

 by not planting sweet potatoes on or near infested fields. In 

 some localities it would })ay to abandon the crop over a large 

 area for two or three vears in order to starve out the weevils. 



